Regulation of compressor cylinder capacity



Dec. 13, 1960 J. K. WELCHON 2,964,235

REGULATION OF COMPRESSOR CYLINDER CAPACITY Filed Nov. 21, 1957 2 Sheets-Sheet 1 PI-IAsE TIMING DEVICE I DIRECT CURRENT FIG. 3.

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Dec. 13, 1960 J. K. wELcHoN 2,964,235

REGULATION OF COMPRESSOR CYLINDER CAPACITY Filed Nov. 21, 1957 2 sheetsfsheet 2 United States Patent'O REGULATION oF COMPRESSOR CYLINDER CAPACITY James K. Welchon, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Nov. 21, 1957, Ser. No. 697,832

4 Claims. (Cl. 230-25) This invention relates to reciprocating compressors. In one aspect it relates to means for unloading or for providing capacity regulation for cylinders of reciprocating gas compressors. In another aspect it relates to a means for providing capacity regulation for gas compressors which is put into operation without having to close down the compressors.

The petroleum industry in general, and specifically the natural gas and gasoline and the oil production industries, use large numbers of reciprocating or piston-type compressors. The gasoline industry uses these compressors for, among other things, compressing hydrocarbon gases prior to extraction of condensible or gasoline boiling range hydrocarbons. The production industry uses compressors among other things, in well fluid gathering systems, for compressing gases in recycling operations and for recycling in gas lift oil production operations.

Power units for operating gas compressors are usually selected to operate at or very nearly at capacity for maximum operating efiiciency and for savings in capital investment. And further, these power units are selected to operate at capacity for compressing gas from an available intake pressure to a desired outlet pressure. For example, a compressor may be designed for compressing gas from a dry gas well for delivery to a gas transmission pipe line. When the well is new, the reservoir pressure may be sufiiciently high to allow the well to deliver gas to the transmission line without compression. As the well is produced, the reservoir pressure will decline, due to the withdrawal of gas from the reservoir, and com pression of the gas may be necessary to maintain deliveries. As the reservoir pressure declines further, the quantities of gas available for compression will also decline, but because of the lower pressures the gas will require more compression. Thus according to the invention it will be possible to compress larger volumes of gas at relatively high intake pressures or smaller volumes at lower intake pressures but with constant horsepower output by the prime mover. With a single compressor design, it will be possible to operate a gas well compressor delivering gas to a transmission line without change in the compressor design throughout the economic life of the gas well.

In an oil producing field, gathering lines are laid to collect gas from a plurality of gas-oil separators and to transport the gas to centrally located gasoline plants. At these plants, the natural gasoline and liquefied petroleum gas components are extracted from the gas so collected. 1t frequently happens that booster stations, or booster compressors are required in the gathering lines at points intermediate the gas-oil separators and the central gasoline plant. Because each of these booster stations 'serves relatively small numbers of wells, there often is considerable fluctuation in the inlet gas pressure to the compressors. It is desirable that these compressors be able to accommodate these pressure changes with a minimum of attention from an operator. In fact many such installations are normally unattended with only an 2,964,235 rtentedp 9 attendant present for short intervals each day to make routine checks, such as, on the oil and water supplies for the prime mover, etc. This invention is particularly well suited to accommodate the fluctuations in pressure at the compressor inlet automatically. In the first example of a gas well declining in output pressure, the compressor constantly compensates for the decreasing pressure with constant prime mover horsepower. In the case of a booster compressor the compensation will be for either an increasing or a decreasing inlet pressure, but in either case, the prime mover horsepower will remain essentially constant.

For oil well gas-lift cycling purposes separator tank pressures frequently vary, thus providing gas of variable pressures for recompression prior to cycling to the gas-lift wells. Compressor cylinders are usually selected so that the power units will be fully loaded when the compressors are operating at an expected low inlet pressure. When gas pressure increases the power units will be overloaded. To prevent overloading of the power units and the possibility of choking them down, the volumetric efficiency of the compressor cylinders should be adjustable to compensate for the possible overload.

According to my invention, I have provided an automatic apparatus for regulating the capacity of a compressor cylinder in response to the pressure of the intake gas to the compressor cylinder.

An object of my invention is to provide an inexpensive means for controlling the volumetric efficiency of gas compressors.

Another object of my invention is to provide an inexpensive means for regulating the volumetric efliciency of gas compressors to keep the compression load at the rated horsepower of the prime movers driving the compressors.

Still another object of my invention is to provide an inexpensive means for regulating the volumetric efliciency of gas compressors when compressor suction pressure has become increased or decreased, in order to maintain the compression load at the rated power output of the prime mover driving such compressors.

Yet another object of my invention is to provide means for regulating the capacity of volumetric efficiency of gas compressors, wherein installation or provision of the means for regulating capacity in no way adversely affects the structure or rigidity of the compressor cylinder.

Many other objects and advantages of my invention will be apparent to those skilled in the art from a careful study of the following description and attached drawing which respectively describes and illustrates a preferred embodiment of my invention.

In the drawing, Figure 1 illustrates an indicator card settingforth the principles upon which my invention is based.

Figure 2 is an elevational view, partly in section, of a portion of the apparatus of my invention.

Figure 3 is a diagrammatic view of another portion of my invention.

Figure 4 is an end view of a portion of the apparatus in Figure 3 looking from the line 4-4.

Figure 5 is a perspective view of a portion of the apparatus illustrated in Figures 2 and 3.

Figures 6, 7 and 8 illustrate alternative embodiments of a portion of my apparatus.

Figure 9 illustrates, diagrammatically, a portion of the apparatus of Figures 2 and 3.

My invention includes apparatus for providing capacity regulation for a cylinder of a reciprocating gas compressor comprising, in combination, a cylinder for a reciprocating gas compressor having an intake and an outlet, a piston fitting said cylinder and being adapted to reciprocate in said cylinder on an intake stroke and on a compression and exhaust stroke, a cam assembly for actuating said in take, a phase timing device, said cam assembly being regulated by said phase timing device in such a manner as to close said intake after the beginning of the compression portion of said compression and exhaust stroke of said piston in response to an increase in intake gas pressure.

Referring now to the drawing, Figure 1 is a pressurevolume diagram, that is, a pressure-volume indicator diagram illustrating the operation of a compressor cylinder with and without capacity regulation.

A common means for adjusting of cylinder capacity for changes in intake pressure involves use of apparatus for addition or subtraction of clearance volume. As an example, in Figure 1, if a compression cycle ABCD is altered to accommodate a higher intake pressure, clearance volume is added so that the compression cycle is A'B'CD'. The amount of clearance volume added is such that the area ABCD is equal to the area AB'CD'. By virtue of the added clearance, the discharge capacity of the cylinder is reduced from DA to D'A.

In contrast tov such means, my invention provides apparatus for regulating the discharge capacity of the compressor cylinder by holding the intake valve open during -a portion of the compression stroke. Thus, the compression cycle is A'A"BCD" and the portion of the compression stroke during which the valve is held open is adjusted so that the area A"BCD" equals the area ABCD. The capacity of the cylinder is reduced from DA to DA", thus reducing the power requirement necessitated by an increase in intake gas pressure.

In Figure 2 of the drawing, reference numeral 11 identifies a compressor cylinder provided with inlet or intake valves 12 and 12a and exhaust or outlet valves 13 and 13a. An exhaust manifold is not illustrated in Figure 2 because that portion of the compressor plays no part in my invention. Any suitable type of exhaust manifold can be used. An intake manifold 14a conducts gas to be compressed from a source, not shown, to valves 12 and 12a. The cylinder is provided with a piston 14 to which is attached a piston rod 15. The piston rod is driven by a prime mover or engine 49 by way of a crank arm 51 and a connecting rod 50. Driven by the engine is a drive shaft 16 to which is attached a drive bevel side gear 20. This bevel side gear is a portion of a differential gear assembly 19. A second driven bevel side. gear 21 is attached to one end of a cam shaft 18. Shaft 16 and cam shaft 18 are illustrated as being supported by bearings 17.

Cams 26 and 27 on cam shaft 18 comprise a cam shaft assembly and are arranged so as to operate valves 12a and 12, respectively, by pushing downward on valve stems 56 and 54, respectively. Compression springs 55 and 53 bias these valves closed. Packing glands 52 make certain that there is no leakage of air into the gas manifold 14a in case pressure within the gas manifold is less than atmospheric. Packing glands 52 also prevent leakage of gas from within the manifold when manifold pressure is greater than atmospheric.

The differential gear assembly 19 is illustrated in Figures 2, 3 and 5. This gear assembly is composed of bevel side gears 20 and 21 and four bevel pinion gears 23. If desired less than four bevel pinion gears, for example, three, two or even a single pinion gear 23 can be used.

.It is preferable, however, to use three or four of these pinion gears in such an assembly. Referring to Figure 2, the bevel pinion gears 23 are mounted rotatably on small shafts 24. Disposed around the outer periphery of this differential gear assembly and attached to the outer ends of the small shafts 24 is a worm gear wheel or floating ring 22. The outer surface of this floating ring or worm gear wheel is provided with threads which mesh operatively with threads on a worm gear 25. Worm gear 25 is disposed at the end of a shaft 28. Shafts 28, 28a and 28b are also supported by bearings 17 which are, if desired, similar to bearings 17 supporting shafts 16 and 18.

The phase timing-device for regulating the timing of the intake valve includes a motor 29, shafts 28a, 28b, pressure gauge 36, drum 34, apparatus operatively connecting these elements and the electrical portion, as illustrated in Figure 3. Reference numeral 29, Figure 3, identifies a reversible electric motor having an armature and one end of which is attached to shaft 28 and the other end is attached to shaft 28a. Reference numeral 30 identifies a gear train which merely serves as a gear reducer for reducing the rotation of shaft 28b with respect to shaft 28a. Shaft 2811, which is attached to the armature of the reversible motor 29, rotates at a high speed relative to shaft 281:. Shaft 28b is intended to rotate only through a relatively small arc, consequently, gear reducer or gear train 3%) is supplied with gears for providing a considerable gear reduction. This gear reducer may be provided with gears to provide a to l or other relatively great gear reduction. A drum 34 is intended to rotate only through a relatively small are such as, for example, 10 to 15 degrees and such small arc of rotation requires a considerable gear reduction in gear train 33.

Drum 34 is constructed of an electrically nonconductive material such as a synthetic polyethylene, or Bakelite, or other plastic which is sufficiently rigid to retain its form throughout long periods of time. Rigidly attached to the outer surface in the relative positions illustrated are a pair of contact metal plates 32 and 33. Plates 32 and 33 are shown as having their longest sides straight lines. However, these sides are, in some instances, curved (Figs. 6, 7 and 8), and concentric (Fig. 6) or not concentric (Fig. 7), or arcs of circles (Fig. 8) or not circu- 'lar arcs (Fig. 6), if compressor design makes such de signs desirable. These plates are separated by a, small distance for accommodation of a movable contact 35 as illustrated. Reference numeral 36 identifies a pressure gauge, for example, a Bourdon tube type (Figures 2, 3 and 9), adapted for sensing pressure of gas to be compressed. A special pressure gauge arm 48 is provided for use with my apparatus. This special arm is consider ably longer than conventional pressure gauge arms which ordinarily extend from a central shaft to calibration markings on the face of the gauge. This long pressure gauge arm 48 is provided with the electrical contact point 35 as mentioned. Upon variation of pressure of gas in the intake manifold 14a, arm 48 and contact 35 move either to the left or to the right and thus the contact 35 will contact either plate 32 or plate 33, depending upon whether pressure in the intake manifold increases or decreases. If the contact 35 moves to the left, a circuit is completed between an electrical lead Wire 37, connecting wire 43, contact 35, plate 32, a connecting wire 57, a coil of a relay 39 and lead Wire 38. When the contact 35 moves to the right, a circuit is completed between lead wire 37, connecting wire 43, contact point 35, plate 33, connecting wire 58, a coil of relay 40 and electric lead wire 38. Under the condition that contact point 35 is between contact plates 32 and 33 neither of these particular circuits is completed. Relay 39 is connected by way of a linkage 41 to switches X and X and relay 40 is connected by way of a linkage 42 to switches Y and Y It is intended that when relay 39 is energized switches X and X are closed and when relay 40 is energized switches Y and Y are closed. Of course when these relays are not energized the respective switches are open, since they are normally open switches. A pair of Wires 46 and 47 conduct electrical current to complete the circuit between wires 37 and 38 and the field windings of the reversible electric motor 29. Wires 44 and 45 lead current to and from the several switches to the armature of the motor.

It is intended that when contact 35 closes the circuit through contact plate 32 the coil of relay 39 is energized and switches X and X are closed, thus completing the circuit from lead wire 37 through switch X and wire 44 point 35 completes a circuit through the contact plate 33, the coil of relay 40 is energized thereby closing switches Y and Y; to complete the circuit between lead wire 38, switch Y, wire 44 to one connection of the armature and the other armature connection to wire 45, switch Y to lead wire 37. This latter direction of current is just the reverse from that previously described when relay 39 was energized, thereby passing direct current through the armature of motor 29 in the reverse direction. Thus, when current is flowing in one direction to the armature of motor 29, the armature rotates in one direction and when the current flows in the opposite direction the armature rotates in the opposite direction, thereby motor 39 is serving as a reversible motor.

The apparatus of my invention is intended to operate in the following manner. Upon increases of pressure of gas in the intake manifold, pressure gauge 36 senses this pressure increase and contact 35 thus moves, for example, to the left and contacts the edge of the contact plate 32, thereby completing the circuit from lead wire 37 through wire 43, contact point 35, plate 32, wire 57, the coil of relay 39 and lead wire 38. Upon energizing the coil of relay 39, switches X and X are closed thereby causing current to fiow through the armature of the reversible motor 29 so as to rotate the Worm gear 25, and the entire differential gear assembly 19 rotates to cause the cams 26 and 27 to be retarded a few degrees behind shaft 16, thereby causing a delayed closing of intake valves 12a and 12. This delayed closing of these intake valves allows a small portion of the gas taken into the cylinder on the intake strokes to be exhausted into the intake manifold at the beginning of the compression strokes thereby partially unloading the cylinder or in other words reducing the amount of gas to be compressed and therefore the power required to compress the reduced charge of gas in the cylinder. As is known in the art, an increase intake manifold gas pressure supplies an increased quantity of gas to the cylinder for compression and of course this increased quantity of gas in the cylinder requires a greater amount of power than normal for compression of the charge. Thus, by unloading a portion of this charge of increased pressure, the power requirement of the engine or prime mover is thus reduced in an attempt to keep the power output of the engine at its rated capacity.

Conversely, when the gas pressure in the intake manifold is reduced, contact point 35 moves to the right and when it moves sufliciently far the contact point 35 touches the edge of the contact plate 33, thereby completing the circuit through the coil of relay 40, thereby closing switches Y and Y which closing allows current from lead lines 37 and 38 to flow through the armature in the opposite direction from that explained when the intake gas pressure was increased. This reversal of current through the armature of the motor causes the armature to rotate in the opposite direction thereby rotating the differential gear assembly in the opposite direction which rotation returns shaft 18 through such an arc with respect to shaft 16 that cams 26 and 27 actuate inlet valves 12:: and 12 in the proper time sequence with respect to the position of the piston so as not to unload the cylinders when the gas pressure has been reduced to the gas pressure which is considered to load fully the compressor and prime mover.

When the gas pressure in the intake manifold 14a is such as to provide the amount of gas which just fully loads the compressor cylinder, the pressure gauge arm 48 is so positioned that contact point 35 is intermediate the adjacent edges of the contact plates 32 and 33 so that electrical contact is not made through either of these plates and their corresponding circuits. When this condition exists, electric current does not flow through the armature of motor 29 in either direction and this apparatus remains in a fixed position. The apparatus remains in this position until the gas pressure in the intake manifold either increases or decreases which increase or '6 decrease causes the pressure gage arin 48to-move in one direction or the other to contact either plate 32 or 33 and cause rotation of the motor and adjustment of the cam shaft 18 with respect to shaft 16 by way of the differential gear assembly 19.

Apparatus part 32a is a portion of drum 34, and is, of course, made of the same electrically nonconductive material as the drum. However, apparatus part 32a is, if desired, a separate piece of apparatus attached rigidly to drum 34 and it can be made of the same material as drum 34 or of other material providing it is a nonconductor of electricity. Apparatus part 33a is similar to part 32a. These apparatus parts are provided so that the drum 34 will not rotate to move plates 32 and 33 out of range of contact point 35. For example, if part 32a were a conductor in contact with plate 32, then if contact 35 touched the long side of the conductor, the drum would rotate to the left when looking in the direction indicated by arrows 4--4 of Figure 3 and contact 35 then upon movement to the right or left would not complete an electrical circuit and the setting of the intake valves would remain fixed irrespective of intake manifold pressure changes. Nonconductive apparatus part 33a is provided for the same reason as just explained for part 3211. Broadly speaking, these nonconductive apparatus parts 32a and 33a make certain that contact 35 is in an operable position at all times with respect to contact plates 32 and 33.

It will be realized that the direction of rotation of cam shaft 18 will be just opposite the direction of rotation of drive shaft 16 because the pinion gears 23 cause the bevel side gear 21 to rotate in the opposite direction from the direction of rotation of the bevel side gear 20.

The sensitiveness of this unloading control apparatus is dependent, among other things, on the sensitiveness of the pressure gage, the distance of the contact 35 from its center of rotation, and the distance the contact 35 has to move to contact plate 32 or plate 33. As long as intake gas pressure remains constant the contact point 35 does not close a circuit through either contact plate. The contact plates are made, for example, of about inch thick brass, or other suitable metal. The contact plates and the contact 35 are made of metal or metals which are resistant to corrosion as occasioned by making and breaking of the electrical circuits.

While certain embodiments of the invention have been described for illustrative purposes, the invention, obviously, is not limited thereto.

I claim:

1. An assembly for providing capacity regulation of a reciprocating gas compressor comprising, in combination, a cylinder for said reciprocating gas compressor having an intake valve and an exhaust valve, a conduit communicating with said intake valve for inlet of gas to be compressed, a piston operatively disposed within said cylinder, an engine operatively connected with said piston, a rotatable cam assembly in operative contact with said intake valve, a differential gear assembly attached operatively to said cam assembly, means operatively connecting said differential gear assembly with said engine, said cam assembly and said differential gear assembly being rotated by said engine to actuate said intake valve, a phase timing device comprising a gas pressure sensing means disposed operatively in said conduit to sense pressure, said pressure sensing means having a first movable electrical contact, second and third electrical contacts spaced from and on opposite sides of said first movable contact and supported on the surface of a rotatable drum, a source of electrical energy, a worm gear disposed in operative relation with the outer periphery of said differential gear assembly, a motor disposed in operative relation with said drum and said worm gear, and an electrical circuit means connecting said source of energy with said contacts and said motor whereby, upon sensing an increase in press sure by said sensing means, said first movable contact contacts one of said second and third contacts thereby completing said circuit to said motor whereby said motor rotates said worm gear and said difi'erential gear assembly to retard closing of said intake valve thereby regulating the capacity of said compressor.

2. The assembly of claim 1, wherein said second and third electrical contacts are elongated edges of plates, said plates being rounded to fit the surface of said drum and said drum having a cylindrical surface, said edges being substantially mutually parallel, said first movable contact being disposed intermediate and at spaced distances from said second and third contacts.

3. The assembly of claim 2 wherein said motor is a reversible motor, and wherein said first movable contact and said second contact comprise a first circuit between said electrical source and said motor, and wherein said first movable contact and said third contact comprise a second circuit between said electrical source and said motor, whereby, upon completion of said first circuit, said motor rotates said differential gear assembly in one direction to retard closing of said intake valve, and upon completion of said second circuit, said motor rotates said differential gear assembly in the other direction to advance closing of said intake valve.

4. The assembly of claim 1 wherein said difierential gear assembly comprises a drive bevel gear and a driven bevel gear, said gears being disposed mutually parallel and spaced. from one another, the beveled portions of said gears facing each other, a beveled pinion gear operatively meshing with the beveled portions of said drive and driven gears in such a manner that said driven gear rotates in an opposite direction from said drive gear, said connecting means comprising a drive shaft operatively connected with said drive gear, a threaded floating ring wheel disposed operably around the aforementioned gears and supporting said beveled pinion gear, a worm gear meshing with said floating ring wheel, said worm gear being fixed rigidly around a. shaft, and said shaft being extended from the armature of said motor.

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